Alkylation of isoparaffins



Filed Aug. e, 1945 [gli @ESN @QQ Patented ay 15, 1945 n UNIT-Bi,

STATI-:s PATENT', oFFlcE 2,375,867 ALxYLA'rIoN or IsoPAnAFms Robert J. Newman. Riverside, lll., assigner to Universal Oil Products Company, Chicago, lll., a corporation of Delaware Application August 6, 1943, Serial No. 497,571 4 Claims. (Cl. Zim-683.4)

This invention relates to the production of branchedhchainsaturated hydrocarbons by the industry. The alleviation of lower boiling par aillns containing atleast one tertiary'carbon atom per molecule, such as isobutane and isopentane, with normally Agaseous oleiins, such as propylene and butylenes, is of particular importance. Among the various alkylation catalysts which have been proposed are aluminum chloride and other metal halide catalysts, hydrogen i fluoride, concentrated sulfuric acid, phosphoric acid, various halosuli'onic acids, etc.

In commercial practice perhaps the most important alkylation reaction involves the interaction of isobutane with various oleiins. Although isopentane, isohexane, etc., are capable of alkylation, these hydrocarbons are in themselves of substantial value and `for that reason are often not available in sufilcient quantities for extensive use in alkylation processes. Although isobutane is commonly alkylated with ethylene,` propylene, and butylenes to produce branched chain hexanes, heptanes, and octanes, it is also possible to alkylate isobutane with the higher boiling or normally liquid oleiins such as amylenes, hexenes, heptenes, etc. An' isobutane alkylation process which is of particular importance at the present time involves the interaction of isobutane with a cracked gasoline fraction containing sub--- stantial quantities of normally liquid oleiins. By this method of operation the cracked gasoline may be converted to a substantially saturated or low olefin content fraction which is then suitable for use as a base stock in aviation gasoline by blending with high octane number alkylate, isopentane, and tetraethyllead. X

In many refineries the limiting factor in any isobutane-olefin alkylation process usually lies in the amount of isobutane which is available. In fact, there is often such a deilciency of available isobutane that it is necessary to resort to special methods for its production, e. g., by the isomerization of normal butane.

One object of the present invention is to pro- 'is to provide a convenient method for the recovery and utilization oi.' isopentane found in cracked gasoline fractions.

Broadly, the invention comprises alkylating isobutane with amylenes, separating isopentane from the alkylation products, separately alkylating said isopentane with propylene, and supplying isobutane produced in the isopentane alkyiation step to said iirst named alkylation step..v

In one specific embodiment the invention comprises alkylating isobutane with an amylene-containing cracked gasoline fraction in the presence of hydrogen fluoride, separating isopentane from the alkylation products, alkylating said separated isopentane with propylene -in a separate alkylation zone in the presence of hydrogen fluoride under alkylating conditions such that substantial amounts of isobutane are formed, separating isobutane from the alkylation products of said last named alkylation step, and supplying said separated isobutane to said first named alkylating step.

The usual components of aviation gasoline are a low olen content base stock, a high Aoctane number blending agent such as alkylate, suillcient isopentane to meet vapor pressure requirements. and the required amount of tetraethyllead. The base stock often consists of a substantially saturated straight run fraction, but in present day practice it has' been found that base stocks having high aromatic contents are preferred. One of the most important methods in the production of aromatic containing base stocks comprises the catalytic cracking of hydrocarbon oils followed by retreatmentof the gasoline boiling range prodcracked gasoline fractions often contain substantial amounts of valuable isopentane. However, this isopentane is not easily recovered since it is usually present in admixture with amylenes having boiling points very close to that of isopentane. By the process of the present invention the amylenes present in a cracked gasoline fraction are interacted with isobutane leaving the isopentane behind in such form that it can be separated readily by fractionation from the alkylation' products. Moreover, I have found that, particularly in the presence of a .hydrogen iiuoride catalyst, substantial amounts of isopentane are produced as a by-product during the alkylation of isobutane with amylenes. According to this invention the total isopentane which can thus be rey available for interaction with further quantities' of cracked gasoline.

This invention is based on the experimental discovery that when isobutane is alkylated with amylenes and when isopentane is alkylated with propylene in the presence of a suitable catalyst and under suitable conditions substantial amounts of isopentane and isobutane are produced, respectively. The extent to which these side reactions occur will depend upon many factors especially the catalyst and operating conditions employed. In the case of isobutane-amylene alkylation, the greatest amount of isopentane is produced when a hydrogen fluoride catalyst is employed, and the isopentane production is extensive over a relatively wide range of operating conditions. In the case of isopentane-propylene Y alkylation, I have found that greater amounts of isobutane are formed at higher temperatures and higher mol ratios of isopentane to propylene as hereinafter described in greater detail.

Although the preferred catalyst for the interaction of lsopentane with propylene is substantially anhydrous hydrogen fluoride, it is possible to employ catalysts containing as much as about 10% water. In fact, the commercially available anhydrousl hydrogen fluoride generally contains up to about 2% by weight of water. Excessive dilution with water is undesirable since it tends to reduce the alkylating activity of the catalyst and introduces corrosion problems. It is alsowithin the scope of my invention' to employ hydrogen fluoride containing relatively minor amounts of various additives or promoters such as boron triiluoride.

The alkylation oi isoparamns with olens in the presence of a hydrogen fluoride catalyst is ordinarily conducted on a continuous scale by introducing the hydrocarbon charging stock and catalyst into a mechanically agitated reaction zone or any other zone suitable for effecting intimate contact between the hydrocarbons and catalyst. The` hydrocarbon-catalyst mixture is maintained at'the desired temperature and pressure for the required reaction time. It is desirable to maintain a substantial mol excess of isoparamns over olens in the hydrocarbon feed to the alkylation zone in order to promote alkylation as the principal reaction of the process. The reaction mixture is withdrawn and is introduced into a separation zone which ordinarily consists of a gravity settler. The lower catalyst layer is withdrawn and a major portion thereof may be recycled to the alkylation zone although another portion thereof may be withdrawn from the system and subjected to regeneration. Regenerated and/or fresh catalyst is supplied to the alkylation zone to maintain a relatively constant amount of catalyst within the reaction system. The upper hydrocarbon layer from the settler is subjected to fractionation for the recovery of gasoline boiling range products and for the separation of unconverted isoparalns which are recycled to the alkylation zone.

The alkylation of isoparains with olens in the presence of a hydrogen fluoride catalyst is carried out at a temperature of from about F. to about 200 F. although the reaction temperature is preferably within the range of from about 50 F. to aboutl50 F. In the alkylation o! isopentane with propylene it is preferred to employ temperatures in the upper portion oi' this range, namely, from about 75 F. to about 150 F. in order to favor the production o! isobutane during the reaction. The pressure on the alkylation system is ordinarily just high enough to maintain-the hydrocarbons and catalyst in substantially the liquid phase, e. g., from about 50 to about 500 pounds per square inch. The time factor in .the alkylation process is conveniently expressed in terms of space time" which is defined as the volume oi' catalyst within the contacting zone divided by the volume rate per minute of hydrocarbon reactants charged to the zone. Usually the space time will fall within the range of from about 5 to 80 minutes although in certain cases it may be desirable to extend this range in either direction. It is preferable to maintain at all times a substantial mol excess of isoparamns over oleflns in the hydrocarbon feed to the alkylation zone, e. g., from about 3: 1 to about 10:1 or higher. In order to promote the formation of isobutane during the alkylation of isopentane with propylene in the presence of hydrogen iiuoride it. is desirable to maintain a mol ratio oi' isopentane to propylene greater than 5:1, e. g., from about 5:1 to about 20:1. In general the volumetric ratio of hydrogen fluoride catalyst to hydrocarbons in the contactingzone should b'e about 1:1 although ratios of from about 0.5:1 to about 2.0:1 will given-Butane 0.4 Iso-amylenes 16.8 n-Amylenes '1.9 Iso-pentane- 29.6 n-Pentane 2.5 Cs and higher 42.8

This cracked gasoline fraction has a bromine number of and contains 41% by weight oi' oiens. In scheme I, barrels of isobutane are reacted with as much of the cracked gasoline fraction as possible. In. scheme II, 100 barrels of isobutane are alkylated with the cracked gasoline fraction, but in addition the available ilopentane in the alkylation products is separated and alkylated with propylene to produce isopentane-propylene alkylate and a substantial amount of isobutane which is recycled to the mst alkylation zone and therein becomes available for alkylating additional quantities of the cracke gasoline fraction.

In scheme I the total available isobutane comprising 100 barrels per day is interacted with 159 barrels per day of the cracked gasoline fraction. The alkylation is conducted in the presence of a hydrogen fluoride catalyst at 100 F., 180 pounds per square inch, 37 minutes space time, and a mol ratio of isoparamn to olenn in the charge of about 8.1. From this step there is a total production of 142.0 barrels per day of isobutane alkylate, 8.3 barrels per day of normal pentane. and '14.4

barrels per day ot isopentane. For the sake' of comparison it is shown in scheme I that there are 69.0 barrels per day of excess cracked Sasoline fraction and 17.4 barrels per day of unused propylene which would be utilized in'the process of the present invention as shown in scheme II.

In scheme II the same quantities of available isobutane, cracked gasoline fraction, and propylene are shown. In the first alkylation zone 100 barrels per day of isobutane and 228 barrels per day of cracked gasoline fraction are charged. A hydrogen uoride catalyst is employed under substantially the same conditions as described in connection with scheme I. From this operation there is recovered 107 barrels per day of isopentane. This isopentane comprises the isopentane originally present in the Cas-200 F. cracked gasoline and also the isopentane produced during the alkylation reaction. The 107 barrels per day of isopentane is alkylated with 17.4 barrels per day of propylene in a separate alkylation zone employing a hydrogen uoride catalyst at 100 F., 220 p. s. i., 35 minutes space time, and a mol ratio of isopentane to propylene of about 7:1. In addition to 67.5 barrels per day of isopentane-propylene alkylate producted in the latter alkylation step there is also a production of 43.6 barrels per day of isobutane which as shown is recycled to the first alkylation step. It

is obvious that the recycle of this additional isobutane permits the utilization of an additional 69 barrels per day of cracked gasoline fraction. The overall result in scheme II is the production of 204.0 barrels per day of isobutane alkylate. 9.1 barrels per day of normal pentane, and 67.5 barrels per day of isopentane-propylene alkylate.

'Ihe advantages oi the present invention are summarized in the following comparison of the two schemes:

Table Scheme I Scheme ll Holy- It is evident that the production of isobutane alkylate is increased by approximately 44% in scheme 1I and in addition a considerable quantity oiisopentane-propylene alkylate is obtained. It will be seen that my invention provides a convenient solution to a serious problem which arises during the commercial operation of the alkylation process, namely, the shortage of isobutane. The invention enables the rener to utilize readily Aavailable propylene i'or the production of a satisfactory isopentane-propylene alkylate while at the same time producing additional quantities of isobutane which can be reacted with cracked gasoline to increase the overall yield of aviation gasoline stock from a given quantity of available hydrocarbon reactants.

I claim as my invention:

1. An alkylation process which comprises alkylating isobutane with amylene to form alkylated isobutane and isopentane, separating isopentane from the resultant products, alkylating the separated isopentane with propylene in the presence of hydrogen fluoride at a temperature oi' from about 75 F. to about 150 F. while maintaining a molar ratio of isopentane to propylene of i'rom about 5:1 to about 20:1, whereby to produce a substantial amount of isobutane concurrently with the alkylated isopentane, and supplying the isobutane thus produced to the iirst-mentioned alkylating step.

2. An alwlation process which comprises subjecting isobutane and a cracked gasoline fraction containing amylene and isopentane to alkylating conditions to react amylene with isobutane, separating isopentane from the resultant products, alkylating the separated isopentane with propylene in the presence of hydrogen uoride at a temperature of from about 75 F. to about 150 F. while maintaining a molar ratio o! isopentane to propylene of from about 5:1 to about 20:1. whereby to produce a substantial amount of isobutane concurrently with the alkylated isopentane, and supplying the isobutane thus produced to the rst-mentioned alkylating step.

3. The process as dened in claim 1 further characterized in that the mst-mentioned alwlating step is effected in the presence oi hydrogen fluoride catalyst.

4. The process as deiined in claim 2 further characterized in that the first-mentioned alkylating step is effected in the presence of hydrogen uoride catalyst.

ROBmT J. l'. 

